1. Field of the Invention
The present invention relates to a charged beam exposure apparatus, a charged beam control method and a manufacturing method of a semiconductor device.
2. Related Background Art
A charged beam exposure apparatus comprises a function of drawing a pattern with a high resolution because it is capable of drawing with a resolution on a wavelength level of charged particles (e.g., electrons or ions) shorter than a light wavelength. On the other hand, since the charged beam exposure apparatus directly draws a completed pattern with a small divided pattern beam in a manner different from that in a mask drawing method by light exposure, this apparatus has a problem that drawing takes a long time. However, as the charged beam exposure apparatus has a feature of being capable of forming a highly accurate thin line pattern, it has been making progress as a leading tool for a next technique of a light exposure type lithography technique or for manufacturing of semiconductors of many kinds in a small amount such as an application specific integrated circuit (ASIC). Methods of directly forming a pattern with an electron beam include a variable shaped beam (VSB) drawing method in which a pattern is drawn with an electron beam that has passed through a stencil aperture, as well as a method in which an entire wafer surface is scanned while turning on/off of a small circular beam is controlled to form a pattern. There has also been an electron beam drawing technique of a collective drawing type which has developed from the VSB drawing wherein repetitive patterns constitute one block, and a stencil is prepared in which the patterns corresponding to a plurality of blocks are formed, and then the stencil is selectively used to achieve high-speed drawing.
Since the VSB type electron beam exposure apparatus improves a beam resolution, there has heretofore been employed a method in which a highly accelerated electron beam is implanted into a resist on the wafer (e.g., Japan Patent Laid-open No. 2002-353128). Further, Japan Patent Laid-open No. 2002-353128 discloses a technique wherein current density is increased to increase a drawing speed, while a brightness control aperture provided with a plurality of opening patterns is disposed at a position where the electron beam forms a crossover in the vicinity of an exit of a condenser lens, in order to prevent a beam blur due to a space charge effect, and brightness is controlled by selecting the aperture.
However, in the high accelerating voltage method, a proximity effect occurs, and this is a phenomenon in which an applied electron beam is reflected by various kinds of multiplayer thin films formed on a lower surface of a resist on a wafer upper surface and again directed upward from the resist. As a result, the drawn pattern is blurred and the resolution is deteriorated. Thus, in the high accelerating voltage type charged beam exposure apparatus, control to compensate for the proximity effect is essential, thus requiring not only an optical system, but also a large-scale system in respect of control. Consequently, there has been a problem that the system is complicated to induce more troubles, leading to decreased accuracy. Moreover, since highly accelerated electrons are used, the wafer surface might be damaged.
In order to overcome the problems described above in the VSB method with a charged beam at a high accelerating voltage, an aperture type electron beam drawing method has been proposed which uses an electron beam at a low accelerating voltage (e.g., Japan Patent Laid-open No. 2000-173529).
In the highly accelerated charged beam exposure apparatus, the beam blur due to the space charge effect caused between a first shaping aperture and a second shaping aperture is at a negligibly low level, so that when high-resolution drawing is performed, the brightness can be controlled in accordance with an amount of a current passing through the second shaping aperture or most of the beam can be cut by variably shaping it in the second shaping aperture, thereby decreasing a beam current after the second shaping aperture to perform drawing.
However, in the low accelerated charged beam exposure apparatus, the beam blur due to the space charge effect caused between the first shaping aperture and the second shaping aperture is at a high level. To solve such a disadvantage, when the aperture for the brightness control is disposed at a crossover position to control brightness, for example, as shown in Patent document 1, there are problems that if the number of small openings is increased to obtain a uniform beam on a sample, contamination accumulated on a surface thereof changes an opening area to prevent a stable beam current from being obtained and that a charge-up is caused on the contamination to cause drift of the beam.
Furthermore, in Japan Patent Laid-open No. 2002-353128, a brightness control mechanism is disposed in a space of an illumination optical system closer to an electron beam gun side than the first shaping aperture. However, in the exposure apparatus using the electron beam at the low accelerating voltage, because the beam drift due to disturbance (a magnetic field, an electric field) is large, an optical system is reduced in size and a path of the electron beam is shortened to control the beam drift, so that it is difficult to newly and additionally provide a beam current control mechanism in the light path.
Still further, in a conventional electron beam exposure apparatus, a blanking operation is performed by a blanking deflector disposed on a wafer side of the first shaping aperture and by a blanking aperture. However, a voltage applied to a selective deflector can vary between its rising edge and falling edge. There has also been a problem that if this variance of timing satisfies a particular condition, the electron beam passes through the blanking aperture, and the resist on the water is unwillingly exposed to light.